A T cell is a type of lymphocyte, or “white blood cell”, that mediates the cellular immune response to foreign macromolecules, termed antigens. While T cells are necessary for normal mammalian immune responses, in some instances it is desirable to inhibit their activation: for example, in some autoimmune diseases, the T cells of a subject respond to “self-antigens”, i.e., macromolecules produced by the subject, rather than foreign-made macromolecules, and damage the cells and tissues of the subject.
Autoimmune T cell responses are found in subjects having systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), insulin-dependent diabetes and multiple sclerosis (MS) and contribute to the pathophysiology of each.
T cells also cause graft rejection and graft versus host disease (GVHD). Graft rejection is caused by an immune response against the transplanted tissues (the graft), which are recognized as “foreign” by T cells of the recipient (host). Graft versus host disease is caused by engrafted T cells, which recognize host-made macromolecules as “foreign.”